trophoblast tro·pho·blast (trō'fə-blāst')n. The outermost layer of cells of the blastocyst that attaches the fertilized ovum to the uterine wall and serves as a nutritive pathway for the embryo. Also called trophoderm.

(trō'fə-blāst') The outermost layer of cells of the blastocyst, which attaches the fertilized ovum to the uterine wall and serves as a nutritive pathway for the embryo. The trophoblast eventually differentiates into such tissues as the amnion, the placenta, and the umbilical cord.